We investigated why liver mitochondria from small mammals are leakier to protons than those from larger mammals. Sixty-nine percent (+/-23%) of the proton leak differences appeared to relate to membrane area (less inner membrane surface area in larger animals); any residual differences must reflect differences in membrane properties. There were differences in phospholipid fatty acid composition; unsaturation index, monounsaturates, palmitate (16:0), stearate (18:0), docosahexaenoate [22:6(n-3)], and the 22:6(n-3)/22:5(n-3) ratio all correlated with body mass. Proton flux per square centimeter did not correlate significantly with body mass or, in general, with phospholipid fatty acid composition, suggesting little role for fatty acid composition in determining proton leak in mammals of different body mass. However, unsaturation index and n-3 polyunsaturated fatty acid content correlated significantly with proton leak per milligram phospholipid when literature data from reptiles and rats in different thyroid states were included, giving some support to suggestions of a general role for phospholipid fatty acid composition in determining mitochondrial proton leak.

Resting O2 consumption of hepatocytes isolated from mammals ranging in mass from 20-g mice to 200-kg horses decreases with increasing body mass. The substrate oxidation system increases in activity with increasing body mass and mitochondrial proton leak and phosphorylation system decrease in activity, resulting in a higher mitochondrial membrane potential in hepatocytes from larger mammals. The absolute rates of O2 consumption due to nonmitochondrial processes, substrate oxidation, mitochondrial proton leak, and the phosphorylation system decrease with increasing body mass. These decreases are due partly to a decrease in mitochondrial number per cell and partly to decrease in mitochondrial inner membrane proton leakiness and in ATP turnover by cells from larger mammals. Quantitatively, the proportion of total cell O2 consumption by nonmitochondrial processes (13%) and oxidation of substrates (87%) and the proportions used to drive mitochondrial proton leak (19%) and the phosphorylation system (68%) are the same for hepatocytes from all mammals investigated. The effect of matched decreases in the rates of proton leak and of ATP turnover is to keep the effective amount of ATP synthesized per unit of O2 consumed relatively constant with body mass, suggesting that the observed value is optimal.

Hepatocytes were isolated from nine species of mammal of different body mass (and standard metabolic rate). The cells were incubated under identical conditions and oxygen consumption measured. The rate of oxygen consumption (per unit mass of cells) scaled with body mass with exponent -0.18. In general, there was a 5.5-fold decrease in oxygen consumption rate with a 12,500-fold increase in body mass. The decrease in oxygen consumption rate was not due to an increase in cell volume with increasing body mass but to a decrease in intrinsic metabolic activity of the cells. This novel finding confirms and explains the decrease in oxygen consumption rate measured in tissue slices from larger mammals by H. A. Krebs (Biochim. Biophys. Acta 4: 249-269, 1950) and recently by P. Couture and A. J. Hulbert [Am. J. Physiol. 268 (Regulatory Integrative Comp. Physiol. 37): R641-R650, 1995].

Due to limited availability of pharmacological therapies, triple-negative breast cancer (TNBC) is the subtype with worst outcome. We hypothesised that 2-Deoxy-D-Glucose (2-DG), a glucose analogue, may hold potential as a therapy for particularly aggressive TNBC. We investigated 2-DG’s effects on TNBC cell line variants, Hs578T parental cells and their isogenic more aggressive Hs578Ts(i) 8 variant, using migration, invasion and anoikis assays. We assessed their bioenergetics by Seahorse. We evaluated metabolic alterations using a Seahorse XF Analyzer, citrate synthase assay, immunoblotting and flow cytometry. We assessed the cancer stem cell (CSC) phenotype of the variants and 2-DG’s effects on CSCs. 2-DG significantly inhibited migration and invasion of Hs578Ts(i) 8 versus Hs578T and significantly decreased their ability to resist anoikis . Investigating 2-DG’s preferential inhibitory effect on the more aggressive cells, we found Hs578Ts(i) 8 also had significantly decreased oxidative phosphorylation and increased glycolysis compared to Hs578T. This is likely due to mitochondrial dysfunction in Hs578Ts(i) 8 , shown by their significantly decreased mitochondrial membrane potential. Furthermore, Hs578Ts(i) 8 had a significantly increased proportion of cells with CSC phenotype, which was significantly decreased by 2-DG. 2-DG may have benefit as a therapy for TNBC with a particularly aggressive phenotype, by targeting increased glycolysis. Studies of more cell lines and patients’ specimens are warranted.

The cannabinoid 1 (CB1) receptor regulates appetite and body weight; however, unwanted central side effects of both agonists (in wasting disorders) or antagonists (in obesity and diabetes) have limited their therapeutic utility. At the peripheral level, CB1 receptor activation impacts the energy balance of mammals in a number of different ways: inhibiting satiety and emesis, increasing food intake, altering adipokine and satiety hormone levels, altering taste sensation, decreasing lipolysis (fat break down), and increasing lipogenesis (fat generation). The CB1 receptor also plays an important role in the gut–brain axis control of appetite and satiety. The combined effect of peripheral CB1 activation is to promote appetite, energy storage, and energy preservation (and the opposite is true for CB1 antagonists). Therefore, the next generation of CB1 receptor medicines (agonists and antagonists, and indirect modulators of the endocannabinoid system) have been peripherally restricted to mitigate these issues, and some of these are already in clinical stage development. These compounds also have demonstrated potential in other conditions such as alcoholic steatohepatitis and diabetic nephropathy (peripherally restricted CB1 antagonists) and pain conditions (peripherally restricted CB1 agonists and FAAH inhibitors). This review will discuss the mechanisms by which peripheral CB1 receptors regulate body weight, and the therapeutic utility of peripherally restricted drugs in the management of body weight and beyond.